Matrix isolation spectroscopic study of the free radical HCCN

Abstract

The free radical HCCN was produced in an Ar matrix via photolysis of its precursor diazoacetonitrile, NNCHCN, with radiation of wavelengths longer than 350 nm. The ir spectra of HCCN and three isotopic modifications (DCCN, HC13CN, and HCC15N) were obtained, and normal coordinate analyses based on two different geometries, bent and linear, were carried out. The results provide a determination of the general valence force field, and favor the linear, allenic configuration H–Ċ=C=Ṅ. The electronic spectrum of HCCN in an argon matrix was also obtained. A tentative assignment of the band system observed in the uv part of the spectrum has been made.

The ν1 + ν5 Band of HCCN: Determination of the ν5 Vibrational Energy

“…A hot band involving the upper state 1 ϩ 5 , specifically 1 ϩ 5 -5 , had been observed previously (13) with its origin at 3226.597 cm Ϫ1 . Earlier estimations of the energy of the 5 Ϫ1 found a number of lines with a time profile typical of the radical HCCN as shown in Fig. 1a and 1b.…”

“…The primary interest was on whether this molecule is linear or bent; thus, most investigations have focused on the HCC bending potential. Early experimental studies based on matrix isolation EPR (1-4) and infrared spectra (5) indicated that HCCN is a linear triplet molecule in its ground electronic state. This was supported by analysis of the millimeter spectrum of HCCN in the gas phase reported by Saito et al (6).…”

“…Furthermore, a high-resolution study of the 1 CH stretch by Morter et al (13) and a millimeter wavelength study of the pure rotational transitions by McCarthy et al (14) both found several low-lying HCC bending vibrational states, which were evidence for quasilinearity. By means of relative intensity measurements, these investigators estimated the lowest excited vibrational energy, 5 for potential barriers from the two isotopes might be expected. Because of the nearly factor of two change in the reduced mass for the vibration on deuteration, 5 of HCCN would be expected to sample different regions of the potential curve from DCCN.…”

“…By means of relative intensity measurements, these investigators estimated the lowest excited vibrational energy, 5 for potential barriers from the two isotopes might be expected. Because of the nearly factor of two change in the reduced mass for the vibration on deuteration, 5 of HCCN would be expected to sample different regions of the potential curve from DCCN. In this paper, we report the assignment and analysis of the HCCN combination band, 1 ϩ 5 , obtained by highresolution infrared kinetic spectroscopy in the region 3323 to 3383 cm Ϫ1 .…”

Accurate ab initio quartic force fields of cyclic and bent HC2N isomers

“…Early experiments by Dendramis and Leroi using matrix infrared (IR) and ultraviolet (UV) spectroscopy concluded the radical to be linear by performing a normal mode analysis 16 . Additionally, Saito et.…”